Models & Migrations — Django

Defining models

python

# courses/models.py
from django.db import models
from django.contrib.auth.models import User

class Category(models.Model):
    name  = models.CharField(max_length=100)
    slug  = models.SlugField(unique=True)

    class Meta:
        verbose_name_plural = "categories"

    def __str__(self):
        return self.name  # shown in admin and shell


class Course(models.Model):
    LEVEL_CHOICES = [
        ("beginner",     "Beginner"),
        ("intermediate", "Intermediate"),
        ("advanced",     "Advanced"),
    ]

    title       = models.CharField(max_length=200)
    slug        = models.SlugField(unique=True)
    description = models.TextField(blank=True)
    category    = models.ForeignKey(Category, on_delete=models.CASCADE, related_name="courses")
    author      = models.ForeignKey(User, on_delete=models.SET_NULL, null=True)
    level       = models.CharField(max_length=20, choices=LEVEL_CHOICES, default="beginner")
    is_live     = models.BooleanField(default=False)
    created_at  = models.DateTimeField(auto_now_add=True)
    updated_at  = models.DateTimeField(auto_now=True)

    class Meta:
        ordering = ["-created_at"]

    def __str__(self):
        return self.title

Migrations — syncing models to the database

bash

# Create migration files (based on changes to models.py)
python manage.py makemigrations

# Apply migrations — actually create/alter the database tables
python manage.py migrate

# See all migrations
python manage.py showmigrations

# Every time you change models.py:
# 1. python manage.py makemigrations
# 2. python manage.py migrate

Common field types

python

# String fields
models.CharField(max_length=200)     # short text, max_length required
models.TextField()                   # long text, no limit
models.SlugField()                   # URL-friendly string

# Number fields
models.IntegerField()
models.FloatField()
models.DecimalField(max_digits=10, decimal_places=2)

# Boolean and null
models.BooleanField(default=False)
models.NullBooleanField()            # True / False / None

# Dates
models.DateField()
models.DateTimeField()
models.DateTimeField(auto_now_add=True)  # set on create
models.DateTimeField(auto_now=True)      # set on every save

# Files
models.ImageField(upload_to="covers/")
models.FileField(upload_to="uploads/")

# Relationships
models.ForeignKey(Category, on_delete=models.CASCADE)    # many-to-one
models.ManyToManyField(Tag)                              # many-to-many
models.OneToOneField(User, on_delete=models.CASCADE)     # one-to-one